This application is based on application No. 2000-0031965 filed with the Korean Industrial Property Office on Jun. 10, 2000, the content of which is incorporated hereinto by reference.
(a) Field of the Invention
The present invention relates to an epoxy resin composition for using a nonflammable thin copper film laminate, which is applied to a printed circuit board (PCB), and a laminate using the same.
(b) Description of the Related Art
In conventional epoxy resin composition, an amine-based curing agent and a curing prompter have been generally used as well as brominated difunctional and multifunctional epoxy resins as the main material. The brominated epoxy resin has been used to bring non-flammability, and trifunctional or multifunctional epoxy resin has been also used to increase heat-resistance and mechanical strength. However, since the cure reaction does not occur easily with the use of only epoxy resin, the epoxy resin may be cured by adding a curing agent into the epoxy resin, and activating the epoxy group.
At present, dicyandiamide has been generally used as a curing agent, however imidazole is generally added as a curing catalyst, since the reaction rate of dicyandiamide with epoxy resin is very slow, in the case where the dicyandiamide is only used. U.S. Pat. Nos. 5,308,895, 5,508,328, 5,620,789, and 5,721,323 show that boric acid is added as a cure retarder in order to increase a glass-transition temperature, by controlling a curing rate and increasing a curing degree due to increase to a curing density. However, dicyandiamide is used as a curing agent, and the glass-transition temperature (Tg) is between 140xc2x0 C. and 160xc2x0 C.
Since a coordinate bond with the boric acid and the imidazole at low temperatures prevents the imidazole from curing the epoxy resin, the epoxy resin has an improved stability at room temperature, and the coordinate bond inhibits curing the epoxy resin at low temperatures. In general, the boric acid and imidazole decompose with each other at 120xc2x0 C. or greater, the decomposing imidazole improves the reactivity of dicyandiamide, and a ring-open of epoxy group is prompted due to the increase in reactivity. As a result, the curing rate of the epoxy resin increases, and then the glass-transition temperature increases.
However, the use of dicyandiamide requires organic solvents such as dimethylformamide (DMF), and N-methyl 2-pyrrolidone, which are harmful to the human body, due to the solubility of dicyandiamide, and also requires stable storage, since the dicyandiamide deposits at low temperatures. As well, heat-resistance of the epoxy resin and the dicyandiamide is limited at 250xc2x0 C. or above, since the dicyandiamide is pyrolyzed by itself at 200xc2x0 C. or above. In addition, there is an increase in the dielectric constant of the epoxy resin, that results from adding dicyandiamide.
Accordingly, in the case where imidazole prompts the ring-open of the epoxy resin without the use of dicyandiamide, and epoxy polymer reaction occurs through the chain-reaction of the epoxy group, a thin copper film laminate that has a glass-transition temperature in the range of 170xc2x0 C. or greater and improved heat-resistance may be fabricated, since the polymer bond gets to be strong, the curing density can increase. In addition, the thin copper film laminate has decreased dielectric constant than the conventional one. However, the epoxy resin composition for the thin copper film laminate, as mentioned above, has not appeared.
The heat-resistance of nonflammable epoxy resin for using thin copper film laminate is represented by the glass-transition temperature, and the epoxy resin having a glass-transition temperature in the range of 120xc2x0 C. to 150xc2x0 C. has been generally used as a FR-4 product. As the glass-transition temperature is higher, the epoxy resin has a better heat-resistance due to the high curing density of epoxy resin, a suitable size at high temperatures due to small heat expansion, lower absorbability to water due to dense molecular structure. Therefore, a thin copper film laminate may be manufactured, compared to a polymer resin having low glass-transition temperature. In order to increase the glass-transition temperature, certain methods have been applied where epoxy resin having a trifunctional group or a multifunctional group is added, novolac epoxy is added, and BT resin or polyimide is blended.
The present invention is made in consideration of the problems of the prior art, and it is an object of the present invention to provide a nonflammable epoxy resin composition for a thin copper film laminate, having an improved heat-resistance due to the increase to a glass-transition temperature of 170xc2x0 C. or greater, which results from an epoxy polymer reaction that is prompted to a ring-open of epoxy group by imidazole without use of dicyandiamide.
It is another object to provide the nonflammable epoxy resin composition for a copper thin film laminate, having low dielectric constant, and a laminate using the same.
It is another object to provide the nonflammable epoxy resin composition for a copper film laminate, that is prepared without use of a harmful solvent to human body, and a laminate using the same.
It is another object to provide the nonflammable epoxy resin composition having a controllable gelation time through controlling a curing rate of epoxy resin and a laminate using the same.
In order to achieve these objects, the present invention provides a nonflammable epoxy resin composition for using a thin copper film laminate comprising:
a) brominated bis-phenol A-type difunctional epoxy resin;
b) multifunctional epoxy resin;
c) an imidazole-based curing catalyst; and
d) a curing retarder.
The present invention also provides a thin copper film laminate, that comprises a fiber glass laminate impregnated with one or more epoxy resins, and the thin copper film located on the outer of the fiber glass laminate, wherein the fiber glass laminate and the thin copper film are united with each other.
In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventors of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature, and not restrictive.
The epoxy resin composition of the present invention, which is used for a thin copper film laminate of a nonflammable impregnated fiber glass laminate, is cured by imidazole catalyst, due to a ring-open of epoxy group, instead of the conventional dicyandiamide.
The bis-phenol A-type epoxy resin of the present invention comprises bromine, that is preferably from 15 wt % to 55 wt %, and the bromine brings non-flammability into a thin copper film laminate, and the equivalent ratio of epoxy group is preferably from 300 to 1500.
In addition, the multifunctional epoxy resin of the present invention has three or more epoxy functional groups per molecule, that is trifunctional, and tetrafunctional and novolac resin as a general multifunctional epoxy resin. In general, as the functional groups increase, the epoxy resin has greater glass-transition temperature.
The epoxy resin needs a curing agent in curing process, and an amine-based curing agent has been used as a conventional curing agent, that has a problem on solubility to an organic solvent, and requires sophisticated processes. Accordingly, as supplement to the conventional curing agent, the curing agent of the present invention includes imidazoles, such as 1-methyl imidazole, 2-methyl imidazole, 2-ethyl 4-methyl imidazole, 2-phenyl imidazole, 2-cyclohexyl 4-methyl imidazole, 4-butyl 5-ethyl imidazole, 2-methyl 5-ethyl imidazole, 2-octhyl 4-hexyl imidazole, 2,5-choloro-4-ehtyl imidazole, and 2-butoxy 4-allyl imidazole, and imidazole derivatives.
The content of the imidazoles is preferably based on 0.1 to 20 weight part, compared to 100 weight part of epoxy resin (the total weight of difunctional epoxy resin and multifunctional epoxy resin), and more preferably based on 1 to 5 weight part.
The use of imidazoles increases the gelation rate of epoxy resin, and epoxy resin is uneasy to mold, since the gelation time is shorter to 200 seconds or less. Therefore, a curing retarder is used in order to control the gelation rate, and increase the gelation time to 200 seconds or more, and the curing retarder brings convenience to mold. The curing retarder includes boric acid, salicylic acid, hydrochloric acid, sulfuric acid, oxalic acid, terephthalic acid, isophthalic acid, phosphoric acid, lactic acid, phenyboric acid, and toluene sulfuric acid, and the amount of the curing retarder used is preferably from 0.1 to 10 equivalent weight per mole based on equivalent weight per mole of imidazole, more preferably from 0.5 to 5 equivalent weight per mole of imidazole.
Though the epoxy resin of the present invention may be used with multifunctional epoxy resin in small amounts, the present invention has glass-transition temperature in the range of 170xc2x0 C. or greater, since the curing rate and curing density of epoxy resin are controlled by adding the imidazole, respectively as a catalyst, and a curing retarder. Therefore, it can manufacture nonflammable thin copper film laminate having strong heat-resistance. In addition, the use of imidazole may not need the use of an amine-based curing agent such as dicyandiamide, which has a low solubility to an organic solvent, and an undesirable property at high temperatures, and also may not need the use of a harmful solvent to the human body such as DMF on the curing process. Therefore, the process may be environmentally desirable, and the dielectric constant may decrease.
While the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.